Filter plates are used in filter presses for dewatering suspensions or slurries. In a filter press, a row of filter plates forms a solid plate pack of sealed filter chambers with two filter cloths in between each pair of plates. Process fluids are supplied to each filter chamber via one or more inlet channels and filtrate is discharged from each filter chamber via one or more outlet channels.
When starting a filtration cycle, the filter plates are first pressed tight against each other to seal the filter chambers. During a filling step, slurry to be dewatered is pumped via a slurry inlet channel into all filter chambers simultaneously. During a filtration step, solids are captured by the filter cloth to form a filter cake. At the same time, liquid penetrates through the filter cloth and the filtrate is drained from the filter chamber via one or more drainage outlets. A filter plate of a pressure filter can comprise an inflatable membrane. During a squeezing step, the membrane is inflated by pressurized medium, such as compressed air or pressurized water, to impose mechanical compression via the membrane on the filter cake, thus reducing the moisture content of the cake. During a washing step the filter cake is washed by impelling washing liquid to the cake and discharging the washing filtrate. During a drying step, compressed air is forced through the filter cake to achieve low residual moisture content before the filter cake is finally removed from the filter chamber.
The drying air is under pressure when it is fed into the filter chamber, where it pushes residual liquid through the filter cake. In the filter chamber, the pressure of the drying air reduces and the air expands.
Current filter plate packs are bearing the risk of unequal chamber conditions after the filtration step. The unequal conditions include inadequate thickness of the filter cake, uneven cake distribution in a single filter chamber, or uneven cake distribution over the plate pack length. This results in differences in air flow in individual chambers during the air drying step. Some chambers can take very high air flows because of total or partial short cuts. High air flow through a filter chamber causes a high risk of filter plate erosion and other damages.